Two-Color Electric Field Resolved TransientGrating Spectroscopy
of anOligophenylenevinylene Dimer
Andrew M. Moran.1 JeremyB. Maddox,2 Janice W. Hong,3 Jeongho
Kim,' ReneA. Nome,' Guillermo C. B~3 Shaul Mukarnel,z NorbertF.
Schererl
IDepartment of Chemistry, The University ofChieago, Chicago, IL
60637, USA2Department of Chemistry, The University ofCalifomia at
Irvine, Irvine, CA 92967, USAJDepartment of Chemistry, The
University of Cali fomi a at Santa BMbara, Santa Barbara,CA 93106,
USA
E-mail: [email protected]
Abstract. Two-color transient grating signals for an
oligophenylenevinylene dimer andmonomer are measured using spectral
interferometry. It is shown that the spectral phasesof the signals
are particularly sensitive to nuclear dynamics and relaxation.
The introduction of diffractive-optics (DO) technology to
femtosecondnonlinear ·spectroscopy experiments has allowed for
heterodyned signal detectionat optical frequencies with passively
phase-stabilized interferometers. I The firstDO-based transient
grating (TG) experiments utilized wavelength-integratedheterodyne
detection.2 More recently, optical photon-echo spectra have
beenobtained for a variety of systems with spectral
interferometry.3-~ We have usedspectral interferometry and TG
spectroscopy in studies of chemical relaxationdynamics,6.7 solute
and solvent signal field resolution,8 and high·ftequencyvibrational
resonances by broadband coherent Raman emission.9 The presentwork
is a comparative study of nuclear relaxations dynamics for
conjugatedmonomer and dimersysterns.
The molecules considered here are a highly-symmetric
paracycyclophanelinked oligophenylenevinylene dimer (5Rd) and its
monomer constituent (5R) for'which linear absorption spectra are
given.6 It should be noted that the spectra ofour 510 and 550 nm
probe pulses overlap with the fluorescence bands of 5R and5Rd.
These molecules do not absorb pignificantly at wavelengths longer
than 500nm in their ground states.
Details for our home-built. amplified 1 ld!z Ti:Sapphite laser
system and.four·wave mixing interferometer· are given elsewhere.6
Pump pulses are producedby second harmonic generation in a 0.2 rom
BBO crystal and are centered at 405nm with 70 fs duration. Tunable
probe pulses are generated with a home-builtnoncollinear optical
parametric amplifer. which yields 25-35 fs pulses from 500-700
nm.
Spectrograms of the experimentally measured signal pulses are
computedusing
(1)
where Es (7:) is the signal field and we take g(t -7:) to be a
gaussian function with Iwidth equal to the probe pulse duration. In
our notation, T is the experimentally controlle(delay between the
pump and probe pulses and t is absolute time. where t=O is defined
a~the time the peak of the probe pulse arrives at the sample.6
Signal spectrograms fOIdegenerate ftequency experiments are
presented in the top row of Figure I. The signa.emission times for
5R (5Rd) are t=1 I fs (t=IG fs) and t=4 fs (t=O fs) for pulse
delays ofT={fs and T=500 fs, respectively. Nuclear relaxation is
taken to be complete at T=500 flbecause evolution oftbe signal
spectrograms is not observed after T-200 fs. Spectrogralrufor
experiments with 510 urn probe pulses are presented in the middle
row of Figure 1.The signal emission times for 5R (5Rd) are t=4 fs
(t=1 fs) and t=-2 fs (t=-3 fs) for pulsedelays of T=O fs and T=500
fs. respectively. The signal field of 5Rd is more positivelychirped
at T=O than at T=500 fs. whereas the time-frequency shape for 5R is
insensitive ttJthe pulse delay. Data collected with probe pulses
cemered at 550 Dm are displayed in thebottom row of Figure L The
signal emission times for 5R (SRd) are t=-2 fs (t=-3 fs) andt=-4 fs
(t= 5 fs) for pulse delays ofT=O fs and T=500 fs. respectively.
T=O fs T=500 fs T=O fs T=500 fs
4.T1"._~""; :~ .•. ~•. : :~ .•••~•.• : ~ .•• ~••
.. ;0 : .. 0 . ': .. 0 '...4.6~·· .: '.'; : .. :: : '{-••.• ~
•.•.•• ~ ••. , •.••.•.•.•.•. " ••. -,. •.••.•.•.•••. , •.•••. ,.
••••.••••.••. 'I." •.
-40 0 40 80 -40 0..-..~
1:3 3.81'~ :
--: 3.7 .?8
4080
-40-;20 0 20·40-40-20 0 20 40-40-20 a 20 40--40-20 0 20 40
t (fs)
Figure.1. Spectrograms for 5R and 5Rd computed using Equation
(I). The delaybetween the pump and probe pulses, T, is given at the
top of each column. 70 fspump and probe pulses centered at 405 nm
were used to obtain the data in the firstrow. The data in the
middle row were collected with 70 fs,405 nm pump pulsesand 30 fs,
520 nm probe pulses. Measurements in the bottom row were
acquiredwith 70 fs. 405 nm pump pulses and 25 fs. 550 nm probe
pulses. The chemicalspecies is indicated in each panel.
This qualitative modelpredicts that positive emission timeof
relatively large magnitudesshould be observed when the
pro~frequency is tuned to the resonancefrequency. In con~
negativesignal emission times with smallmagnitudes are obtained
wheti'theprobe pulse is tuned to the wing ofthe resonance. The data
presentedin Figure 1 exhibit this behavior.
The greatest change in thesignal emission time as a function
0pulse delay is observed in theexperiment with degenemte 405
runpulses. This experiment is sensitiveto nuclear motion in regions
ofcoordinate space that exceed the
bandwidth of the probe pulse spectrum through the
dispersivecotnpOnent of thesignal phase.
Figure 2. Absorptive (solid) anddispersiye (dashed) projections
ofthe nonlinear polarization. Theemission time (dotted) is
computedas the group delay with Re{PP}}.
-:::s
ci-6
------
,m •••Emission time
.--- ~.. ~, ., ...,.3
AcknowledgmentsThis research was supported by the NSF (CRE
0317009 and NIRT ERC0303389).
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